Thomas Eisner

Thomas Eisner, who died on March 25 aged 81, was an entomologist who achieved
international renown for his analysis of how insects use chemicals —
including love potions, nerve drugs and scalding jets of toxic liquids — to
attract mates, deter predators and trap and kill prey.

Insects and arthropods (spiders, millipedes and so on) appear highly vulnerable to a wide range of predators, but many survive. Eisner wanted to know how. Before his work, for example, only a few insects were known to have chemical defences.

As a child living in Montevideo he noticed how secretions discharged by millipedes and craneflies had a particular noxious smell and stained his fingers brown. He came to suspect that their recipe for survival might be the rule rather than the exception, an intuition that opened a research field which kept him busy throughout his life.

A professor at Cornell University from the 1950s, Eisner was probably best known for his studies of the bombardier beetle, a small ground-dwelling insect found in the tropics. Eisner was a graduate student when he encountered the beetles, which made popping sounds and squirted out a liquid with the same pungent smell remembered from his past.

Soon afterwards he met a chemist who was researching the chemicals produced by the craneflies he had handled as a boy. She told him that the smell was due to a group of chemicals called benzoquinones. Another friend told him he had discovered that, when agitated, a cockroach species also produced benzoquinones.

Eisner felt that the chemicals must have some special purpose if such different species were producing them. He first tested how the cockroach sprayed the chemical in response to a simulated attack on a leg; he found the spray was surprisingly directional. He then turned his attention to the bombardier.

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With the aid of slow-motion photography, Eisner and his colleagues ran experiments showing that the beetle shoots its spray with uncanny accuracy, that the spray is hot (100ºC) and fired in pulses of 500-1,000 drops a second, like a machine gun.

Further research revealed that the beetle has separate sacs in its abdomen, one for hydrogen peroxide and one for a quinone. When the contents are mixed together, an explosive reaction takes place, liberating oxygen, which is used as a propellent to fire the acidic brew several inches from the insect with an explosive popping sound via a little double-barrelled turret under the insect’s abdomen. The noise and cloud of hot, foul-smelling liquid are usually enough to see off predators.

The insect’s defences were not foolproof however. One species of toad swallows bombardiers whole and Eisner once heard the beetle discharge, too late to do any good, inside a toad’s belly.

Eisner’s work on the bombardier became the focus of a skirmish between Darwinians and Creationists who claimed that such an ingenious system proves that evolution, based on the idea that all mutations are random, could not be the whole story. But evolutionists pointed out that Eisner had identified many “intermediate” relatives of the bombardier which share a large number of its attributes apart from the explosive chemicals. It is entirely possible, as Eisner argued, that any one of these, with their ready-made “gun turrets”, could have evolved with the additional advantage of the explosive chemicals, without the intervention of an intelligent, God-like designer.

Thomas Eisner was born on June 25 1929 in Berlin. His father, a pharmaceutical chemist, was Jewish and the family fled the Nazis in 1933, moving to Spain. The Spanish Civil War caused them to move again, first to Paris, then to Montevideo, Uruguay, then, in 1947, to New York.

During these moves Thomas developed a strong interest in natural history. He collected caterpillars, beetles and maggots, housing them in his bedroom.

He studied at Champlain College, Plattsburgh, transferring to Harvard University two years later. After taking a degree in 1951 he stayed on to do doctoral research in Entomology and became a lifelong friend of the evolutionary biologist Edward O Wilson. In 1957 he moved to Cornell, where he remained for the rest of his career.

Eisner’s discoveries were often triggered during walks, when he would notice an insect doing something curious, then hypothesise why and take his hypothesis back to the lab for testing with the help of scientific colleagues.

Among other discoveries, Eisner noticed that in the act of copulation the male rattlebox moth gives his female partner lifelong protection against being devoured by voracious spiders. When a spider traps a female in its web, the moth secretes a noxious chemical in a froth of bubbles, and the spider promptly liberates the moth by cutting the web away with its fangs. When the female casts about to select a mate, she has a way of sensing which males are richest in the protective chemical she needs — and those are the ones she chooses.

In other studies, Eisner found that the whip scorpion fends off its enemies with a spray of concentrated acid which penetrates the predator’s skin; that some millipedes gas their enemies with hydrogen cyanide, while others hurl small pads covered with Velcro-like bristles to tangle up their legs; that aquatic beetles emit a potent repellent when caught by fish, causing the predators to spit them out; that palmetto beetles use adhesive feet to glue themselves to leaves; that the European blister beetle manufactures the aphrodisiac Spanish Fly as a defence mechanism, while the male beetle, Neopyrochroa flabellata, must absorb enough of it from the blister beetle for it to ooze out of a cleft-shaped organ on his head, otherwise females of the species refuse to mate.

More sinisterly, he found that the female of one firefly species that does not naturally produce toxic substances lures males of a species that does by faking its mating signal and then, when a male shows up, kills and eats him, acquiring both dinner and immunity from attack. “Insects won’t inherit the Earth,” Eisner once said. “They own it now.”

A talented pianist, Eisner kept an upright piano in his laboratory and would often play it to aid thinking. He won the American National Medal of Science in 1994 and the Tyler Prize for Environmental Achievement in 1990.

In 2004 he published For Love of Insects, a semi-autobiographical account of his life’s work, with a foreword by Edward O Wilson and a book-jacket portrait of the author riding backwards on a bicycle.

He married, in 1952, Maria Lobell, an electron microscopist who collaborated in his research; she survives him with their three daughters.